Conventionally, as a method of controlling an injection molding machine that variably controls the number of rotations of a drive motor in a hydraulic pump, that, based on this, drives and controls a hydraulic actuator such as an injection cylinder (a hydraulic cylinder) and that controls operation processes in a molding cycle, a method of controlling an injection molding machine that is disclosed in Patent literature 1 is known.
In such a control method, when the number of rotations of the drive motor in the hydraulic pump is variably controlled and thus the operation processes in the molding cycle are controlled, as the hydraulic pump, a hydraulic pump is used in which at least a plurality of fixed discharge flow rates can be set, the fixed discharge flow rate corresponding to each operation process is preset based on predetermined conditions and, during a molding operation, the hydraulic pump is switched to the fixed discharge flow rate corresponding to each operation process, with the result that the number of rotations of the drive motor is variably controlled and thus the operation processes are controlled. With this control method, it is possible for the drive motor to use the hydraulic pump as at least either a small-capacity hydraulic pump or a large-capacity hydraulic pump. Advantageously, this makes it possible to, for example, eliminate an additional measure for an unstable condition in which the number of rotations of the drive motor is decreased or to reduce the level of such a measure, with the result that energy saving can be enhanced and the running cost can be reduced; this also makes it possible to decrease the size of the drive motor (servo motor) to reduce the initial cost of the entire machine including a servo circuit and the like; and, furthermore, this also makes it possible to stabilize the control to improve moldability and molding quality.